1. Field of the invention:
This invention relates to a method of mounting electronic components with or without leads to designated positions on a printed circuit board.
2. Description of the prior art:
According to a conventional method wherein electronic components with or without leads are glued to a printed circuit board to form an electronic circuit, adhesive is first deposited to designated positions on the printed circuit board, and thereafter, the electronic components are glued to the electrodes on the printed circuit board using a components-feeding device, the printed circuit board thus produced then being delivered to the drying and soldering steps.
However, in order to deposit adhesive to designated positions on a printed circuit board, either of the following methods must be selected: a depositing tool such as a dispenser is arranged in parallel with a components-feeding head, and two printed circuit boards are separately fixed in position on two stations, respectively, of a board feeding device, before performing the adhesive-depositing and components-mounting steps; or different pieces of equipment are used to perform the respective steps separately. In either method, there is a limit to increasing the speed of mounting components as long as the deposition of adhesive and the feeding of components are performed using two stations.
Japanese Laid-Open Patent Publication Nos. 56-66095 and 58-53887 disclose systems incorporating an adhesive depositing step into a components-feeding station. The former uses a method in which adhesive is applied to an electronic component held in a magazine, the magazine with the component held therein then being mounted on a head to feed the component. This system, however, requires an independent mechanism for depositing adhesive to the electronic component, and is complex in construction, therefore, it has difficulty in increasing the speed of mounting components.
On the other hand, as shown in FIG. 4, the latter system employs a rotary head having a nozzle 1 on a rotating periphery thereof, with a chuck 4 for holding a sucked electronic component 3 provided in a sleeve 2 surrounding the nozzle. As shown in FIG. 3, this system interposes two steps, i.e., a component position-correcting step C (centering) and an adhesive-depositing step D, between the step A of sucking an electronic component from an electronic components-delivery section and the step B of mounting the component.
When the adhesive-depositing step (D) is incorporated in the process between the component-sucking step (A) and the component-mounting step (B), it is necessary in practice for the chuck to hold the component to fix it in position before adhesive is being deposited thereto. With this system, since the component is held in position from two directions by the chuck 4 provided in the sleeve of the nozzle, misalignment of the component sucked onto the tip of the nozzle with respect to a dispenser for depositing adhesive may be prevented when adhesive is deposited to the underside of the component.
However, the above construction involves the following two problems in connection with the recent trend toward the speed-up of the mounting of electronic components of multiple kinds.
First, if the rotary head is operated at high speed, residual vibration remains on the tip of the nozzle when the head temporarily stops during its intermittent rotating motion, with a resultant relative vibration in the adhesive-depositing step, causing misalignment of the position of the dispenser for depositing adhesive with respect to the component held between the tip of the nozzle and the claws of the chuck, thereby causing adhesive to be applied to the chuck claws. Adherence of foreign matter to the chuck claws will lead to misfeeding of components, thus subtantially deteriorating the mounting reliability in practical use.
Secondly, for mounting components of various kinds and different sizes ranging from microchips to ICs, a plurality of nozzles of different sizes which can be selected should be provided in one station. Thus, when using a rotary head, a plurality of nozzles of such different sizes should be attached to the head, and accordingly chucks corresponding to the respective nozzles should be mounted around the nozzles. In practice, however, it is difficult to attach chucks to such a plurality of nozzles of different sizes mounted on the single head.